In ultrasound strain elastography an image of relative axial strain, which is associated with tissue stiffness differences, is displayed. This strain image (also called elastogram), can for example help to distinguish lesion malignancy. An estimation of axial strain requires some axial compression (or de-compression) in the form of a relative axial motion between transducer element(s) of an ultrasound probe and the anatomical site (e.g. a patient's (deeper) tissues). Such compression can be provided by the weight of the ultrasound probe and/or by physical pressure applied by the user of the system (e.g. medical staff or a doctor) and/or by internal patient motion due to heartbeat or breathing. A sensitive elastography system can require very little motion (e.g. a relative axial motion in the order of 10 μm). More compression can tend to improve the strain image quality, until degrading effects such as de-correlation, blurring or misregistration can become dominant (e.g. around a relative axial motion of about 1 mm). Because the required (slight) relative axial motion for ultrasound elastography may approach the limit of the user's physical perception and/or because it may affect the quality of the strain image, an elastography system can be able to display an indication of the quality of the strain image. This indication can for example be a (non-quantitative) bar graph next to the strain image.
An exemplary elastography system displaying such bar graph is the Philips iU22 system. For example, the brochure “Sensitivity and strength, Philips Breast Elastography Ultrasound Quick Start Guide, Philips, 2010” (e.g. currently to be found at http://www.healthcare.philips.com/main/products/ultrasound/technologies/elastography.wpd), which is a quick start guide providing a brief overview of the Philips iU22 breast elastography system, discloses that a real-time compression feedback bar is displayed next to the strain image. This on-screen indicator provides the user with real-time feedback on the appropriate amount of deformation for the elastogram. The system computes the level of resulting tissue deformation and displays it as a green and grey bar to indicate appropriate (green) and inappropriate (grey) tissue deformation for a quality elastogram.
There is a need to further improve such elastography system.